I would always give a quote for full heating, then a quote for boiler change only, if doing full system all workmansip, PIPEWORK and material is guaranteed for one year
If boiler swap only " a system pressure test on existing will be carried out at 2bar, if would be reasonable to expect a sound system not to fail at this pressure therefore any failure of the existing system and subsequent repair due to the test will not be covered by quote or guarantee and repairs will br chargeable, only material supplied and fitted by me is covered by my guarantee, and no existing PIPEWORK , valves or radiators etc is covered in any way if as a result of increased system pressure ( which is normal and expected) there is a leak, please note that any subsequent structural or fabric damage is not covered by either guarantee or PIL
Haha when you read it back it will put some customers off, but that's too bad, cause if its not written down and accepted they will not pay for extra work and expect you to pick up the tab for leaks later on, which will be electrician call out, joiner and painter